1. Priority Information
This application claims priority from European Patent Application No. 03077439.2, filed Aug. 4, 2003, the contents of which is herein incorporated by reference in its entirety.
2. Field of the Invention
The present invention relates to lithographic apparatus and methods
3. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. including part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion all at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
A conventional lithographic apparatus may be found for example, in U.S. Pat. No. 6,271,606, which describes a stage assembly including linear motors for moving an object in at least one direction whereby the object table is enclosed by a chamber.
A lithographic apparatus generally includes both a short stroke accurate positioning unit and a large stroke displacement unit for the object table. In general, the stage provided with the patterning device has large displacements in only one direction while the stage provided with the substrate has large displacements in a plane. In general, the object table provided with the patterning device or the substrate is connected to a first drive unit including a plurality of actuators or linear motors. These actuators or motors allow accurate displacement of the object over a small range. The first drive unit is usually mounted on a second drive unit that allows large displacements in at least one direction. This second drive unit may, for example, include a linear motor or a planar motor. Within a lithographic apparatus, the projection process often takes place in a purified conditioned atmosphere or in vacuum. For maintaining these conditions, the object table may be placed in an enclosing chamber. In the lithographic apparatus disclosed in U.S. Pat. No. 6,271,606, the enclosed chamber still contains at least one part of a commutating motor for large displacements. Since such motors are generally quite large and heavy, their presence inside the conditioned compartment is not advisable. An additional complication may be the requirement of a bearing for the part of the commutating motor located inside the enclosed chamber. Furthermore, it is desirable to keep the compartment in which the conditioned atmosphere is required as small as possible.